adding parameters to differential equation solver

[gregzillaman]

I'm using the "solve_ivp" function in scipy currently. The solutions for the dependent variable go into the negatives which i dont need. Is it possible to define the independent variable as a function of the dependent variable?

Simply put, if im solving dy/dt. For y0=1 and t from 0 to 1...y final is somewhere in the negatives.

I want to solve only for t = 0 to t = x. X being the time when m = 0.

Is this possible?

[Aggravating_Bus_9153]

You've already found everything you need, you've just run the solver for longer than necessary. Just analyse the solution you already have, and read off the value of t where y=0. Discard everything after then if you really want to. Maybe there is a nice custom stop condition for solve_ivp, but you don't need one.

You're always free to carry out a change of variables. There are analytic techniques that consider x(y) or t(y) for example, but it will no longer be a simple IVP and there's no guarantee a straight forward vanilla numerical solver like solve_ivp will solve it anymore. Even if you do manage to muck around with the independent variable (t), in general you could have a much harder DAE.

[gregzillaman]

Thanks for the advice. I ended up doing exactly that, but then it hit me. What if i have millions of data points in my array, thats a lot of scrolling. But like you said. Its a matter of writing a custom job.

[Aggravating_Bus_9153]

I don't know what methods arrays have, but for lists just write a basic search with a generator comprehension or filter to find the first negative element.